1. Field of Technology
The present invention relates to techniques of inserting each of the two low impurity layers (i-layer) into base-collector and base-emitter respectively for a monocrystal Silicon Carbide (SiC) phototransistor, particularly to the construction and fabrication process of the low impurity layer and the phototransistor.
2. Prior Art
As more and more specified electronic devices are requested to operate under severe conditions, the demand of high-gain solid state sensing elements workable at high temperature subsequently grows up time to time. Unfortunately, most part of the known high-gain photodetectors, such as avalanche photodiodes (APD), phototransistors (PT), etc are made by using narrow bandgap materials like monocrystal silicon, amorphous silicon, or group III-V compounds. When temperature is elevated, dark current of the mentioned elements will increase rapidly to thus deteriorate photosensitivity thereof, so that, the operating temperature is confined less than 100.degree. C. Pallab Bhattacharya, Semicinductor Opto-electronic devices Englewood Cliffs, N.J.: Prentice Hall, 1944.
The wide bandgap semiconductor materials, such as Silicon Carbide (SiC), diamond, and gallium nitride (GaN), etc have been used to fabricate high temperature electronic elements lately Morkoc, S. Strite, G. B. Gao, M. E. Lin, B. S-verdlov, and M. Burns, "Largeband-gap SiC, III-V nitride, and II-VI ZnSe-based semiconductor device technologies," J. Appl. phys., vol. 76, no. 3, pp. 1363-1398, wherein the relative techniques of SiC is the most matured and most compatible with silicon ICs in fabricating process. SiC do have several vantage features, such as wide bandgap, high electron mobility, and high thermal conductivity, etc L. Harris, Propertis of Silicon Carbide. London, United Kingdom: INSPEC, the institution of Electrical Engineers, 1995. However, for the time being, the developments of high temperature SiC phototransistors are curbed due to lack of high-gains. This weakness is supposed to be brought about from a drastic recombination of minority carrier in the base of a conventional n-p-n construction thus lower current gain of a transistor and reduce optical gain accordingly B. Casady and R. W. Johnson, "Status of Silicon Carbide (SiC) as a Wide-bandgap Seminconductor for High-Temperature Applications: A Review, `Solid-State Electronics, vol. 39, no. 10, pp. 1490-1422, 1996.
Aiming at the above-depicted defects, the present invention is to propose a newly developed construction and fabrication process for a high-gain monocrystal SiC phototransistor capable of operating at high temperature.